The present invention relates generally to casing valves for use in the casing of a well, and more particularly, but not by way of limitation, to cementing tools constructed for placement in a well casing.
In the drilling of deep wells, it is often desirable to cement the casing in the wellbore in separate stages, beginning at the bottom of the well and working upward.
This process is achieved by placing cementing tools, which are primarily valved ports, in the casing or between joints of casing at one or more locations in the wellbore, flowing cement through the bottom of the casing, up the annulus to the lowest cementing tool, closing off the bottom, opening the cementing tool, and then flowing cement through the cementing tool up the annulus to the next upper stage and repeating this process until all stages of cementing the well are completed.
Cementing tools are shown, for example, in U.S. Pat. Nos. 5,038,862, 5,314,015, 5,526,878 and 3,768,556. Cementing tools often utilize sealing elements to seal between the tool and the wellbore or well casing prior to displacing cement into the well through the tool. For example, many such tools use inflatable packers to seal against the well. Oftentimes, however, inflatable packers have a limited flow area to accommodate the weighted solid laden inflation fluid and do not fully inflate. The result is that the inflatable packer will not hold as much hydraulic pressure as desired. It may be necessary in such situations to wait until the cement below the tool sets up, which is a time-consuming, and therefore costly process. There is a continuing need for stage cementing tools that can be reliably set in the well, to provide for immediate cementing of casing above the tool, with no need to wait for cement therebelow to harden.